Center for Global Development Data Sets
The Center for Global Development is a think tank that focuses on international poverty and inequality and how the policies of developed countries might address those problems. In addition to the center's various research publications and reports, it also hosts various datasets on topics such as aid flows and policies, HIV treatment, and the durability of transitions to democratic government. Additional datasets from the Center are available via its dataverse.
International Monetary Fund Organization and Finances
This IMF site provides various information about the Fund's organization/structure, including information about member countries' quotas of contributions to the Fund. Additional information about IMF funding and transactions with member countries are available via this page on IMF finances. The IMF annual reports are another source for information about IMF finances and transactions with individual countries.
OECD Statistics Portal: Development
The statistics portal of the Organization for Economic Co-operation and Development (OECD) includes a collection of data on development-related activities of OECD members, including very detailed and extensive data on foreign aid.
United Nations General Assembly Committee on Contributions
The General Assembly's Committee on Contributions advises the UN on the distribution of contributions to the UN's budgets across UN member countries, and publishes reports on the status of members' contributions to those budgets. Additional relevant information is also available via the Global Policy Forum's section on UN finances.
U.S. Overseas Loans and Grants ("Greenbook")
To quote the website, the Greenbook shows a complete historical record of United States' (U.S.) foreign aid to the rest of the world by reporting all loans and grants authorized by the U.S. Government for each fiscal year. Data are available in current- and constant-dollar terms. There is also an Explorer for the data that includes both datasets and reports.
World Bank Finances
The World Bank now provides much data about the Bank's finances, including member countries' subscriptions to the Bank and Bank operations during a given year. For additional information about Bank projects in and transactions with individual countries, see the Bank's Projects and Operations data and the Independent Evaluation Group's evaluations of World Bank projects.
World Bank Data Catalog
As part of its Open Data Initative, the World Bank has opened up access to dozens of its data collections and compiled into a single data catalog. The holdings here range from larger databases covering multiple topics to more narrowly-focused collections associated with particular research projects.